Science in the Classroom is a collection of annotated research papers and accompanying teaching materials designed to help students understand the structure and workings of professional scientific research.

Glowy, Bouncy Eggs Teacher Sheet

Introduction

This teacher sheet will provide some background information on the experiment along with the answers to the pre- and post-lab questions the students will receive.

Background Information

The Glowy, Bouncy Eggs experiment introduces students to the chemical properties of eggs and shows them how a chemical reaction between the acetic acid in vinegar and the calcium carbonate of the egg shell results in a rubbery egg. The point to get across to the students is that the acid is what dissolves the egg shell and then coagulates or clumps together the protein membrane underneath to produce the rubber texture. The once brittle egg shell is now replaced by a rubber coating, yet the raw inside of the egg remains. The egg can “glow” at this point when held up to a light because there is no longer an opaque shell. The bubbles that will form when the egg is put in the vinegar is due to the carbon dioxide gas that is produced during the reaction. Students may or may not be familiar with chemical reactions and this may take a little bit of explaining. Examples to consider when explaining this concept are that our stomach acid breaks down or dissolves the food that we eat (larger molecules get broken down into smaller ones) and this is the case with the acid breaking down calcium carbonate into carbon dioxide. Another example is that when acid is added to liquids with protein such as milk, the proteins will clump together and produce curds—this is part of the cheese-making process. This is what is occurring to the protein membrane of the egg once the shell dissolves. The pre-lab questions direct students to start thinking about if it’s the acid that is causing this reaction then would other acidic liquids also do the same to the egg? Here you can introduce what pH is and that it is a value that shows whether a substance is acidic or basic. Consider not going into more detail than this, but stress that the lower the pH something has the more acidic it is and the higher the pH the more basic it is. You can go over some examples of products that are acidic and basic with the class so they get the idea. Have them brainstorm some other acidic liquids they can put the egg in for the experiment. If you are able to get a hold of some pH paper, they can measure the pH themselves or you can search online the pH of the certain liquids.

Pre-lab Questions with Answers

What is the shell of an egg made of? Can you think of anything else that is also made of this chemical? Think “shell.” The egg shell is made of calcium carbonate. Seashells are also made of this and the skeleton of coral reefs.

Is vinegar an acid or base? What is the vinegar going to do to the egg shell? Vinegar is also called acetic acid so it is an acid and it will dissolve the calcium carbonate egg shell.

List some examples of acids and bases.

Acids: lemon juice, coffee, cola, stomach acid, vinegar, etc.

Bases: bleach, ammonia, baking soda, soap, etc.

Draw out the experimental set-up below to include the different conditions you brainstormed.

How are you going to measure/compare you results between conditions? Students will want to make detailed observations with the eggs in these conditions. They can look at the appearance, the amount of bubbling, and size of the egg. At the end of the experiment, they can gently bounce the eggs to see what happens if one bursts over another.

Record below the pH of each of the liquids and answer if it is an acid or base.

Liquid

pH

Acid or base?

What is your prediction on which liquid will produce the more rubbery egg and why? See what they come up with for here. There is no right or wrong answer as long as they can explain why.

Observations

They should record their observations each day of the experiment here. Remember to go over as a class what type of observations they make and the importance of these observations since these are used to draw conclusions at the end of the experiment.

Post-lab Questions with Answers

What do the bubbles coming off the egg represent? Did some conditions have more or less bubbles? The bubbles are carbon dioxide. They can explain here if one condition over the other had more bubbles or less.

In your own words explain what happened to the calcium carbonate in the egg shell when placed in the vinegar. Students should take what they have learned and put it in their own words on what is happening in this experiment.

Using your observations, what conclusions can you make about the different acidic liquids the eggs were put in? They may find here that the acid with the lowest pH produced the more rubbery egg. Either way, there is not a right or wrong answer, they just need to learn how to use their observations to support whatever conclusion they make.

What were the possible sources of experimental error? What would you do differently if you had to set this experiment up again? You may need to explain here what experimental error is. A way to explain this is to have them consider doing this experiment again the exact same way and ask them if they would get the exact same results. The answer should be no. This is due to experimental error in any experiment and that is why in order to have more confidence in your results, experiments need to be performed multiple times. Let them be creative here on how they would set up the experiment again.